The present invention relates to an optical switch for use in optical communication systems or the like and a method of making the same.
With recent developments of optical networks, optical switches are now receiving attention as optical devices of the utmost importance. Also there is a demand for their miniaturization in accordance with the present trend toward increasingly high-capacity optical networks. To meet the demand, a miniaturized optical switch has been proposed which has a movable switching portion formed using micromachine technology. Its structure is depicted in FIG. 1. Reference numeral 10 denotes a silicon (Si) substrate having a groove cut therein by micromachining, wherein there are formed a pair of parallel cantilevers 14a and 14b coupled together at their free ends. Fixedly disposed on the substrate 10 near opposite ends of the cantilevers 14a and 14b lengthwise thereof are guide blocks 11 and 13. Disposed adjacent the guide block 13 is another guide block 12 formed integrally with the cantilever free end coupling portion. The guide block 12 is coated over the entire area of its surface or underside with a soft magnetic film 19c. These guide blocks 11, 12 and 13 have the same height.
An optical fiber 15A is fixed its one end on the guide block 12 and extended and supported across the top of the guide block 11. Two optical fibers 15B and 15C are fixed at one end in parallel to the guide block 13. On the substrate 10 there are mounted magnetic yokes 19a and 19b at both sides of the guide block 12, the magnetic yokes 19a and 19b having wound thereon coils 17a and 17b, respectively. The magnetic yokes 19a and 19b are split centrally thereof and have permanent magnets 18a and 18b inserted between the gaps, respectively.
With the optical switch of such a construction as described above, the application of a driving voltage to, for example, the coil 17a causes it to attract the soft magnetic film 19c coated on the guide block 12 to resiliently bend the cantilevers 14a and 14b toward the magnetic yoke 19a, bringing the light-emitting end of the optical fiber 15A to the position where it stands opposite the light-receiving end of the optical fiber 15B. On the contrary, the voltage application to the coil 17b of the yoke 19b causes the light-emitting end of the optical fiber 15A to stand opposite the light-receiving end of the optical fiber 15C. In this way, light emitted from the optical fiber 15A can selectively be launched into the optical fibers 15B and 15C.
The manufacture of such a conventional optical switch encounters a difficulty in the miniaturization of the magnetic yokes 19a and 19b with the coils 17a and 17b wound thereon; for example, the substrate 10 inevitably becomes as large as 20 by 17 mm or so. It has also been proposed to miniaturize the optical switch by forming optical waveguides in the cantilevers 14a and 14b in FIG. 1, but the proposed optical switch structure still electromagnetically drives the cantilevers and measures about 16 by 18 mm. Besides, the proposed optical switch has a defect that the insertion loss of the waveguide is as large as several dB.
It is therefore an object of the present invention to provide an optical switch that can be driven at a low voltage and hence can be miniaturized, and a method of making such an optical switch.
The optical switch according to the present invention comprises:
substrate means;
fixed electrode means fixedly secured to the substrate means with the surface of the fixed electrode means held lower than and in parallel to the surface of the substrate means;
movable electrode means disposed opposite to the fixed electrode means in spaced relation thereto;
elastic support means for coupling the movable electrode means and the substrate means and for elastically supporting the movable electrode means so that the movable electrode means can be displaced vertically to the surface of the fixed electrode means; and
optical path switching means provided on the surface of the movable electrode means opposite the fixed electrode means and having a light receiving surface vertical to the surface of the movable electrode means;
wherein, by ON-OFF control of voltage application across the movable electrode means and the fixed electrode means, the movable electrode means is displaced toward the fixed electrode means and returned to its normal position to selectively switch the optical path of an incident light beam by the optical path switching means.
The method of the present invention for making an optical switch in which an optical path switching element mounted on a movable electrode is displaced to switch the optical path of an incident light beam, the method comprising the steps of:
(a) forming on a silicon substrate a pattern containing a movable electrode portion and an elastic support portion coupled thereto by a conductive silicon film;
(b) making an opening by etching away that region of the silicon substrate which is opposite to at least the movable electrode portion and the elastic support portion;
(c) attaching a conductive substrate to the underside of the silicon substrate so that one surface region of the conductive substrate serves as a fixed electrode opposite but spaced apart from at least the movable electrode portion in said opening; and
(d) forming the optical path switching element on the movable electrode portion.